Fluid loss additives for well cementing compositions containing a tetrapolymer

ABSTRACT

An additive for reducing water loss from cement comprising a tetrapolymer, a base, an electrolyte, at least one surfactant, and water is disclosed. A process for producing cement slurries with improved water loss properties, as well as an improved method for cementing gas and oil well is also disclosed.

This application is a divisional of application Ser. No. 07/414,961filedSep. 28, 1990 now abandoned which was a continuation-in-part ofapplication Ser. No. 07/029,029, filed Mar. 23, 1987, now abandoned.

The present invention pertains to cement additives which are useful forpreventing water loss from cement slurries. Another aspect of theinvention relates to novel tetrapolymers and the use of said noveltetrapolymers as cement additives. Another aspect of the inventionrelates to cement slurries which have improved water loss properties. Astill further aspect of the invention relates to an improved process forcementing oil and gas wells.

BACKGROUND OF THE INVENTION

Cement compositions are used in the oil and gas industry to cement theannular space in the well bore between the surrounding formation and thepipe or casing. Typically, the cement slurry is pumped down inside thecasing and back up the outside of the casing through the annular space.The amount of water which is used in forming the cement slurry will varydepending upon the type of hydraulic cement selected and the jobconditions at hand. The amount of water used can vary over a wide range,depending upon such factors as the required consistency of the slurryand upon the strength requirement for the particular job.

Many times the hydraulic cement must be placed within or next to aporous medium, for example, shale strate encountered in the well bore.When this happens, water tends to filter out of the slurry and into thestrata during the settling of the cement. Many difficulties are relatedto an uncontrolled fluid loss of this type, such as uncontrolled settingrate, improper placement of the slurry, impaired strength properties,and contamination of the surrounding strata. These conditions are allundesirable in oil and gas well cementing operations.

In order to lessen the loss of fluid from the aqueous cement slurry,various materials have been employed in the past. Unfortunately, thesematerials often have adverse effects upon the cement itself.

For example, U.S. Pat. No. 4,015,991 teaches the use of a copolymer ofacrylamide and 2-acrylamido-2-methylpropanesulfonic acid as a fluid lossadditive for cement slurries. Although this copolymer will reduce thefluid loss from cement slurries, it also has the undesirable effect ofreducing the compressive strength of the cement and of retarding therate at which the cement forms a solid.

A further problem with the fluid loss additives currently available istheir ineffectiveness at temperatures in the range of 300° F. to 450° F.For example, the copolymer described in U.S. Pat. No. 4,015,991 isineffective at a temperature in excess of 250° F.

Thus, it would be a valuable contribution to the art to developadditives which would reduce water loss from cement slurries withouthaving adverse effects upon the compressive strength of the cement orthe rate at which the cement solidifies.

It would also be a valuable contribution to the art to develop additiveswhich would reduce the water loss from cement slurries at elevatedtemperatures.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide additives which willreduce the water loss from cement slurries without reducing thecompressive strength of the cement or delaying the rate at which thecement solidifies.

It is a further object of the present invention to provide additivesthat will prevent the loss of water from cement slurries at elevatedtemperatures.

It is a further object of the present invention to provide a method forreducing the loss of water from cement slurries without reducing thecompressive strength of the cement or delaying the rate at which thecement solidifies.

It is yet another object of the present invention to provide a methodfor reducing the loss of water from cement slurries at an elevatedtemperature.

It is also an object of the present invention to provide cementcompositions having improved water loss properties at elevatedtemperatures.

It is yet a further object of the present invention to provide animproved method for cementing oil and gas wells.

It is additionally an object of the present invention to provide watersoluble polymer compositions which provide improved water lossproperties in cement compositions.

In accordance with one embodiment of the present invention I havediscovered that the addition of tetrapolymers to a cementing compositionwill reduce the water loss from said cementing composition.

In accordance with another embodiment of the present invention, I havediscovered that an additive comprising (A) a tetrapolymer, (B) anelectrolyte, (C) a base, (D) at least one surfactant, and (E) water,will reduce the water loss from cement slurries without reducing thecompressive strength of the cement or delaying the rate at which thecement solidifies. It has also been discovered that this additive willcontrol the water loss from cement slurries at elevated temperatures.

In an additional embodiment of the present invention it has also beendiscovered that tetrapolymers made in a highly energetic polymerizationprocess provides improved water loss control.

DETAILED DESCRIPTION

As used in this application the term tetrapolymer refers to thepolymerization product of at least a four monomer componentpolymerization. The four monomer components suitable for the practice ofthe present invention are:

Component A which has the formula ##STR1## wherein R₁ is hydrogen ormethyl, R₂ is an alkyl amide containing C₂ -C₁₆ alkylene group, an alkylcontaining C₁ -C₁₆ carbon atoms, benzyl, or alkyl benzyl containing C₇-C₁₆ carbon atoms and Me is hydrogen, lithium, sodium or potassium;

Component B which has the formula ##STR2## wherein R₃ is hydrogen,methyl, or ethyl, R₄ is hydrogen, methyl, or ethyl or R₃ and R₄ form acyclic amide;

Component C which has the formula ##STR3## wherein R₅ is hydrogen ormethyl, and R₆ and R₇ are independently hydrogen, methyl, ethyl orpropyl; and

Component D, which has the formula ##STR4## wherein R₈ is hydrogen ormethyl and R₉ is a carboxylic acid, carboxylic salt, ester of acarboxylic acid, sulfonic acid, sulfonate or nitrile.

Suitable examples of component A include but are not limited tocompounds selected from the group consisting of2-acrylamido-2-methylpropanesulfonic acid, salts of2-acrylamido-2-methylpropanesulfonate, alkyvinyl sulfonic acids, alkylvinyl sulfonates, vinyl benzene sulfonic acids, vinyl benzenesulfonates, alkyl vinyl benzene sulfonic acids, alkyl vinyl benzenesulfonates, and combinations of two or more thereof.

Suitable examples of monomer component B include but are not limited tocompounds selected from the group consisting of N-vinyl acetamide,N-vinyl-N-methyl acetamide, N,N-dimethyl acetamide,N-vinyl-2-pyrrolidone, N-ethenyl-N-alkyl acetamide, and combinations oftwo or more thereof.

Suitable examples of monomer component C include but are not limited toethylenically unsaturated N-substituted carboxylic acids selected fromthe group consisting of acrylamide, methyl acrylamidemethylmethacryamide, N-alkylmethacrylamide, N,N-dialkylmethacrylamide,N-alkylacrylamide, N,N-dialkylacrylamide, and combinations of any two ormore thereof.

Suitable examples of monomer component D include but are not limited tocompounds selected from the group consisting of acrylic acid, salts ofacrylic acid, methacrylic acid, salts of methacrylic acid, itaconicacid, salts of itaconic acid, acrylonitrile, alkoxy esters of acrylicacid, alkoxy esters of methacrylic acid, vinyl sulfonate, vinyl sulfonicacid and combinations of any two or more thereof.

As used in this application, the term tetrapolymer broadly refers to awater soluble polymer which is composed of a) from 1 to 60 weightpercent of component B, b) from 1 to 60 weight percent of component C,c) from 10 to 90 weight percent of component A, and d) from 1 to 60weight percent of component D.

One preferred tetrapolymer contains from 30 to 40 weight percent ofN-vinyl-2-pyrrolidone, from 5 to 15 weight percent of acrylamide, from50 to 60 weight percent of sodium 2-acrylamido-2-methylpropanesulfonate, and from 1 to 10 weight percent of acrylic acid.

Currently the preferred tetrapolymer composition comprises a) from about10 to about 61 weight percent of monomer component A; b) from about 10to about 60 weight percent of monomer component B; c) from about 3 toabout 60 weight percent of monomer component C; and d) from at least 10to about 55 weight percent of component D. Additionally, for specificapplications in fresh water and brine water, the following monomercomponent ratios are recommended:

    ______________________________________                                               Monomer Monomer   Monomer   Monomer                                           Component                                                                             Component Component Component                                         A       B         C         D                                          ______________________________________                                        Fresh Water                                                                   125° F.                                                                Broad Range                                                                            10-55     10-40      5-60   10-55                                    Preferred                                                                              20-38     20-30     23-35   14-20                                    Range                                                                         200° F.                                                                Broad Range                                                                            10-55     10-30     15-45   10-20                                    Preferred                                                                              28-38     20-25     23-34   14-15                                    Range                                                                         300° F.                                                                Broad Range                                                                            10-55     10-30      3-60   10-55                                    Preferred                                                                              27-55     10-30      5-35   10-55                                    Range                                                                         Brine Water                                                                   200° F.                                                                Broad Range                                                                            10-55     10-30     15-60   10-30                                    Preferred                                                                              15-45     20-30     20-45   10-20                                    Range                                                                         ______________________________________                                    

The currently most preferred tetrapolymer composition comprises a) fromabout 15 to about 45 weight percent of monomer component A; b) fromabout 10 to about 30 weight percent of monomer component B; c) fromabout 20 to about 45 weight percent of monomer component C; and d) fromabout 10 to about 20 weight percent of monomer component D. Thisparticular tetrapolymer composition is believed to provide the bestwater loss control of any water loss control polymer tested to date.Tetrapolymers of this composition show extremely good water loss controlover a broad range of temperatures in fresh water and brine solutions.The preferred monomers for making this tetrapolymer composition are a)2-acrylamido-2-methylpropane sulfonic acid, sodium2-acrylamido-2-methylpropane sulfonate or, b) N-vinyl-2-pyrrolidone; c)acrylamide; and d) sodium acrylate or acrylic acid.

The tetrapolymers of the present invention can be prepared bypolymerization in accordance with any of the well known free radicaltechniques in solution, suspension or emulsion environment. See, forexample, U.S. Pat. No. 3,547,899, or European patent application No.0115836. In addition, other methods of polymerization known to oneskilled in the art may be employed.

Preferred for the practice of the present invention is thepolymerization of the four monomer components in a highly energeticpolymerization process wherein a significant excess of initiation energyis provided by chemical or electromagnetic means including electrons,gamma rays, x-rays, slow neutrons and ultra violet radiation. Theutilization of excess initation energy appears to result in theformation of consistently better tetrapolymers for use in water losscontrol. By way of guidance but in no way limiting to the presentinvention it has been found that a 100 percent excess of a chemicalinitator such as 2,2'azobis(N,N'-dimethylene isobutyramidine)dihydrochloride is effective to produce tetrapolymers with improvedwater loss control.

The molecular weight of the tetrapolymers of the present invention maybe varied over a considerable range. The molecular weight may be as lowas 30,000 or as high as 1,000,000 or more.

In one embodiment of the present invention I have discovered thattetrapolymers alone or in combination with other additives is veryeffective as a water loss control additive. The tetrapolymers disclosedin this invention are in fact so effective that when provided alone inan effective amount for hydraulic cements, a tetrapolymer may be theonly additive required for water loss control. When utilized as a waterloss control additive in hydraulic cements the tetrapolymer should beemployed in an amount ranging from about 0.1 weight percent to about 5weight percent by weight of dry hydraulic cement, preferably thetetrapolymer will be employed in an amount ranging from about 0.2 weightpercent to about 2 weight percent by weight of dry hydraulic cement. Theweight ranges specified above may be optimized for the particular cementand conditions under which it is utilized.

The monomer ratios as specified above for Fresh Water and Brine Water(at various temperatures) are particularly preferred in cement slurrieswhich will be subjected to conditions similar to those specified above.

Additionally, it has been discovered that an additive comprising (A) atetrapolymer, (B) an electrolyte, (C) a base, (D) at least onesurfactant, and (E) water, will reduce the water loss from cementslurries without reducing the compressive strength of the cement ordelaying the rate at which the cement solidifies. It has also beendiscovered that this additive will control the water loss from cementslurries at elevated temperatures.

Suitable electrolytes (B) for use in the present invention can beselected from the group consisting of sodium, potassium, lithium, orammonium salts of chlorine, bromine, iodine, nitrate, or fluorine. Atthe present time, the preferred electrolyte is potassium chloride.

Suitable bases (C) for use in the present invention include thoseselected from the group consisting of potassium hydroxide, sodiumhydroxide, or ammonium hydroxide. The presently preferred base ispotassium hydroxide.

Suitable (D) surfactants for use in the present invention can beselected from the group consisting of:

1) carboxylates of the formula

    RCOO.sup.- M.sup.+

wherein R is selected from the group consisting of alkyl groupscontaining from 9 to 21 carbon atoms and M is selected from the groupconsisting of sodium, potassium, or lithium;

2) polyalkoxycarboxylates represented by the formula ##STR5## wherein Ris selected from the group consisting of alkyl and alkylaryl groupscontaining from 10 to 21 carbon atoms, M is selected from the groupconsisting of sodium, lithium or potassium, and n is an integer from 5to 21;

3) sulfonates of the formula

    R SO.sub.3.sup.- M.sup.+

wherein R is selected from the group consisting of alkyl groupscontaining from 10 to 20 carbon atoms, and M is selected from the groupconsisting of sodium, potassium, or lithium;

4) alkylbenzene sulfonates represented by the formula

    RC.sub.6 H.sub.4 SO.sub.3.sup.- M.sup.+

wherein R is selected from the group consisting of alkyl groupscontaining from 10 to 20 carbon atoms, and M is selected from the groupconsisting of sodium, lithium, or potassium;

5) lignosulfonates;

6) naphthalene sulfonates of the formula

    RC.sub.10 H.sub.6 SO.sub.3.sup.- M.sup.+

wherein R is selected from the group consisting of alkyl groupscontaining from 3 to 10 carbon atoms, and M is selected from the groupconsisting of sodium, lithium, calcium or potassium;

7) naphthalene sulfonates which have been condensed with formaldehyde;

8) the alpha-olefin sulfonates of the formula

    RC═CHSO.sub.3.sup.- M.sup.+

wherein R is selected from the group consisting of alkyl groupscontaining from 10 to 20 carbon atoms and M is selected from the groupconsisting of potassium, sodium or lithium;

9) poly(ethylene glycol) monomethyl ethers of the formula

    HO--(CH.sub.2 CH.sub.2 O).sub.x CH.sub.3

wherein x can vary from about 20 to about 225,000.

10) polyethylene glycols of the formula

    HO(CH.sub.2 CH.sub.2 O).sub.x H

wherein x can vary from about 20 to about 225,000.

11) alcohol ethoxylates of the formula

    R[OCH.sub.2 CH.sub.2 ].sub.n OH

wherein R is selected from the group consisting of alkyl groupscontaining from 6 to 20 carbon atoms and n is an integer from 2 to 100;

12) alkylphenyl ethoxylates of the formula

    RC.sub.6 H.sub.4 (OC.sub.2 H.sub.4).sub.n OH

wherein R is selected from the group consisting of alkyl groupscontaining from 8 to 15 carbon atoms and n is an integer from 2 to 70;and

13) petroleum sulfonates.

All of these surfactants as well as their methods of preparation arewell known to those skilled in the art. They are available from numerouscommercial suppliers.

At the present time it is preferred that the cement slurry water lossadditive contain two surfactants.

One of the preferred surfactants is poly(ethylene glycol) monomethylether. The surfactant will have a molecular weight ranging from about200 to about 8000, preferably 200 to 1000. Presently Dow Froth 1012®with molecular weight of about 385 is the most preferred.

The other preferred surfactant is a naphthalene sulfonate formaldehydecondensate. Such compounds are also known as sulfonated condensationproducts of formaldehyde and naphthalene or metal salts of condensationproduces of naphthalene sulfonic acid with formaldehyde.

Condensed naphthalene sulfonate formaldehyde condensates suitable foruse in the present invention are marketed by a number of companies undervarious brands and the preparation of some of these are set forth, forexample, in U.S. Pat. Nos. 3,537,869 or 4,814,887. Examples ofcommercially available naphthalene sulfonate formaldehyde condensatesare Lomar D®, CFR-2® Tamol®, SM®, TIC®, and Daxad®. Currently Lomar D®is the preferred naphthalene sulfonate formaldehyde condensate.

At the present time, it is also preferred that the water loss additivecontain (F), a preservative. The nature of the preservative is notcritical to the practice of the present invention and any commerciallyavailable preservative is suitable for use in the present invention. Atthe present time, the preferred preservative is a paraformaldehyde.

The constituents of the water loss additive are present in the followingquantities:

    ______________________________________                                                      Broad Range                                                                            Preferred Range                                                      wt %     wt %                                                   ______________________________________                                        A   Tetrapolymer    0.1-70     1.5-10                                         B   Electrolyte       0.1-37.2 2-10                                           C   Base            0.1-3      .2-2                                           D   Surfactant      0.1-40     5-15                                           E   Water            29-95     70-80                                          F   Preservative (optional)                                                                       0.001-5                                                   ______________________________________                                    

The fluid additive of the present invention is suitable for use with anyhydraulic cement. The term hydraulic cement is meant to encompass anyorganic cement that hardens or sets under water. Hydraulic cements, forexample, include portland cements, aluminus and pozzolan cements, andthe like. The term hydraulic cement is also intended to include cementshaving minor amounts of extenders such as bentonite, gilsonite, and isalso intended to include cements used either without any appreciablesand or aggregate material or such cements admixed with a granularfilling material such as sand, ground limestone, and the like. Thus, forexample, any of the class A-J cements listed in API Spect 10, Section 2,First Ed., January, 1982, are suitable for this purpose. Strengthenhancers such as silica powder can also be employed.

The dry hydraulic cement component, the fluid loss additive of thepresent invention, can be admixed dry or with water to form a pumpable,settable cement slurry. The cement slurry will set to form a monolithicsolid. The water which is employed to form the cement slurry may be anynaturally occurring water suitable for preparing cement slurries. Seawater may be employed and is thus convenient in offshore operations. Itis a particular advantage of the fluid loss additive of the presentinvention that it is effective in reducing fluid loss from cementslurries even where brines are employed to make up the slurry. Thisconstitutes another important advantage of the invention over many othercement additives known in the art.

The amount of water employed to make up the hydraulic cement slurry isnot critical, and generally the amount of water necessary to give asettable cement composition having the required characteristics will bean amount from about 25 to about 150 percent by weight, based on theweight of the dry hydraulic cement. As discussed previously, the amountof water employed should be only such as is sufficient to produce apumpable slurry. Use of the water loss additive of the present inventionmakes it unnecessary to add excess water in anticipation of substantialwater losses.

Generally, the amount of fluid loss additive employed will be in therange of from 0.2 gal to 2.5 gal of additive per 94 lbs. of cementutilized in preparing the cement slurry.

The fluid loss additive of the present invention is suitable for use incement slurries that are subjected to temperatures ranging from 80° F.to 450° F.

In the method of cementing a well bore with the present additive, ahydraulic cement, water and the fluid loss additive of the presentinvention are mixed together to form a pumpable slurry. The cementslurry so prepared is then pumped to the desired location in the wellbore and allowed to harden to form a solid mass.

The following examples are intended to illustrate the advantages of thisinvention, but are not intended to unduly limit this invention.

EXAMPLE I

The purpose of this example is to demonstrate the composition of and amethod for preparing the preferred fluid loss additive of the presentinvention.

The composition of the preferred fluid loss additive system of thepresent invention is represented below.

                  TABLE I                                                         ______________________________________                                        Material             Amount (wt in grams)                                     ______________________________________                                        Water                78                                                       KCI                  2                                                        KOH                  1                                                        Paraformaldehyde     0.02                                                     Sodium naphthalene   9.8                                                      formaldehyde condensate.sup.1                                                 Poly(ethylene glycol) monomethyl                                                                   4                                                        ether.sup.2                                                                   Tetrapolymer.sup.3   5                                                        ______________________________________                                         .sup.1 Lomar D ®, Diamond Shamrock                                        .sup.2 Dow Froth 1012 ®, Dow                                              .sup.3 a poly(sodium 2acrylamido-2-methylpropane                              sulfonateco-N-vinyl-2-pyrrolidone-co-acrylamide-co-acrylic acid),             containing 55 wt % sodium 2acrylamido-2-methylpropane sulfonate, 35 wt %      Nvinyl-2-pyrrolidone, 10 wt % acrylamide, 5 wt % acrylic acid and is          commercially available as HE ® polymer from Phillips Petroleum            Company.                                                                 

A preferred manner of preparing this fluid loss additive is to mix theingredients in the order listed under agitation.

EXAMPLE II

A series of cementing slurry compositions in accordance with the presentinvention and having the compositions as noted in Table II below wereprepared by mixing the additive system of Example I with water and aClass H cement¹.

                  TABLE II                                                        ______________________________________                                                                Amount water loss in                                  Material      Amount    gal/sack of cement                                    ______________________________________                                        Cement A                                                                      Class H cement                                                                              829.85  gm    0.3  gal                                          Water         313.5   ml                                                      Water loss additive                                                                         22.2    ml                                                      Cement B                                                                      Class H cement                                                                              829.85  gm    0.41 gal                                          Water         305.5   ml                                                      Water loss additive                                                                         30.3    ml                                                      Cement C                                                                      Class H cement                                                                              829.85  gm    0.60 gal                                          Water         285.5   ml                                                      Water loss additive                                                                         50.2    ml                                                      Cement D                                                                      Class H cement                                                                              829.85  gm    0.68 gal                                          Water         285.5   ml                                                      Water loss additive                                                                         50.1    ml                                                      Cement E                                                                      Class H cement                                                                              829.85  gm    0.75 gal                                          Water         280.42  ml                                                      Water loss additive                                                                         55.2    ml                                                      Cement F (control)                                                            Class H cement                                                                              829.85  gm    0                                                 Water         335.7   ml                                                      Cement G (control)                                                            Class H cement                                                                              850.96  gm    0                                                 Water         328.9   ml                                                      Cement H                                                                      Class H cement                                                                              645.92  gm    0.41 gal                                          Sand          226.1   gm                                                      Water         284.35  ml                                                      Water loss additive                                                                         23.51   ml                                                      Cement I                                                                      Class H cement                                                                              645.92  gm    0.60 gal                                          Sand          226.1   gm                                                      Water         273.46  ml                                                      Water loss additive                                                                         34.4    ml                                                      Cement J                                                                      Class H cement                                                                              645.92  gm    0.75 gal                                          Sand          226.1   gm                                                      Water         264.86  ml                                                      Water loss additive                                                                         43.0    ml                                                      Cement K                                                                      Class H cement                                                                              829.05  gm     .80 gal                                          Water         275.8   ml                                                      Water loss additive                                                                         58.9    ml                                                      Cement L                                                                      Class H cement                                                                              829.85  gm    1.00 gal                                          Water         261.1   ml                                                      Water loss additive                                                                         73.7    ml                                                      ______________________________________                                    

EXAMPLE III

To demonstrate that the water loss additive of the present inventionwill reduce the water loss from cement slurries over a broad range oftemperatures; the water loss properties of cementing slurry compositionsprepared as in Example II were determined in accordance with API Spec10, Appendix F, First Ed., January 1982.

The following results were obtained.

                  TABLE III                                                       ______________________________________                                                Concentration                                                                 of Additive     Temp.   Fluid-Loss                                    Cement  (gal/94 lbs cement)                                                                           °F.                                                                            cc/30'                                        ______________________________________                                        B       0.41             80     66                                            B       0.41            100     76                                            D       0.68            100     40                                            F (control)                                                                           0.00            100     +1298                                         B       0.41            125     74                                            D       0.68            125     46                                            F (control)                                                                           0.00            125     +1298                                         B       0.41            170     80                                            D       0.68            170     46                                            F (control)                                                                           0.00            170     +1500                                         H       0.41            170     78                                            I       0.60            170     48                                            H       0.41            200     118                                           I       0.60            200     131                                           I       0.60            230     138                                           I       0.60            250     40                                            J       0.75            300     54                                            ______________________________________                                    

The water loss properties of cement slurries prepared without theadditive of the present invention (cement F) were determined attemperatures ranging from 100° F. to 170° F. These cement slurries lostbetween 1298 to 1500 cc of fluid during the 30 minute testing period.

The water loss properties of cement slurries prepared with the additiveof the present invention were determined at temperatures ranging from80° F. to 300° F. These cements only lost from 40 to 138 cc of fluidduring the 30 minute testing period.

Thus, this data demonstrates that the additive of the present inventionprovides cements with superior water loss properties over a broadtemperature range.

EXAMPLE IV

To demonstrate that the fluid loss additive of the present inventiondoes not decrease the compressive strength of the resulting cementcomposition, a series of cement compositions as prepared in Example IIwere tested in accordance with API Spec 10, Section 7, CompressiveStrength Tests, First Ed., January 1982.

The following data was generated.

                  TABLE IV                                                        ______________________________________                                        Concen-        24 Hr COMMPRESSIVE                                             tration        STRENGTH (PSI)                                                 of Additive    @ Atmospheric                                                  (gal/94 lbs    pressure     @ 3000 PSI                                        Cement  of cement) 80° F.                                                                          125° F.                                                                      150° F.                                                                       170° F.                       ______________________________________                                        F (control)                                                                           0.00       1483     3517  4646   4799                                 A       0.30       1483     3725  4697   4713                                 B       0.41       1508     3642  4689   5013                                 C       0.68       1550     3775  5847   6192                                 ______________________________________                                    

Cement F was prepared without the fluid loss additive of the presentinvention. It demonstrated a compressive strength of 1483 PSI at 80° F.during a 24 hour compressive strength test.

Cements A, B, and C were prepared with the fluid loss additive of thepresent invention. They demonstrated compressive strengths rangingbetween 1483 to 1550 PSI. Thus, the additive of the present inventiondoes not decrease the compressive strength of cements.

A similar trend was demonstrated in the tests conducted at 125° F., 150°F., and 170° F.

EXAMPLE V

To demonstrate that the additive of the present invention will reducethe fluid loss from cement slurries which have been formulated with saltwater, a cement slurry B', D', L' and M' were prepared as were CementsB, D, L, and M of Example II except that varying concentrations of saltwater was used to prepare the cementing slurry. For comparative purposesa cement slurry F was prepared as in Example II.

The fluid loss properties of these cement slurries were determined inaccordance with API Spec 10, Appendix F, First Ed., January, 1982.

The following results were obtained.

                  TABLE V                                                         ______________________________________                                                Concentration                                                                 of Additive   NaCL    Temp. Fluid-Loss                                Cement  (gal/94 lbs cement)                                                                         wt. %   °F.                                                                          cc/30'                                    ______________________________________                                        F (control)                                                                           0             0.0     100   +1298                                     B'      0.41          3.0      80   123                                       B'      0.41          10.0     80   134                                       B'      0.41          18.0     80   180                                       B'      0.41          37.2     80   68                                        D'      0.68          3       100   50                                        D'      0.68          3       125   48                                        D'      0.68          3       150   50                                        D'      0.68          3       175   53                                        D'      0.68          10      100   49                                        D'      0.68          10      125   46                                        D'      0.68          10      150   63                                        D       0.68          10      175   66                                        L'      0.80          3       100   43                                        L'      0.80          3       125   45                                        L'      0.80          3       150   48                                        L'      0.80          3       175   42                                        L'      0.80          10      100   49                                        L'      0.80          10      125   52                                        L'      0.80          10      150   54                                        L'      0.80          10      175   56                                        M'      1.00          18      200   94                                        M'      1.00          37.2    100   104                                       M'      1.00          37.2    125   110                                       M'      1.00          37.2    150   122                                       M'      1.00          37.2    175   130                                       M'      1.00          37.2    200   146                                       ______________________________________                                    

Cement F which was prepared without the additive of the presentinvention, exhibited a fluid loss in excess of 1298 cc during the 30minute testing period. The cement slurries prepared with the fluid lossadditive of the present invention only lost from 43 to 180 cc's duringthe 30 minute test period. Thus, the fluid loss additive of the presentinvention will reduce the water loss from cement slurries which havebeen formulated with salt water.

EXAMPLE VI

To demonstrate that the fluid loss additive of the present inventiondoes not retard the rate at which the cement solidifies, cementingcompositions were prepared as in Example II and the rate at which thecement thickens was determined in accordance with API, Spec 10, Section8, First Ed., January, 1982.

The following results were obtained.

                  TABLE VI                                                        ______________________________________                                               Concentration               Thickening                                        of Additive                 Time.sup.1                                        (gal/94 lbs  Temp.   API    (in hours)                                 Cement of cement)   (°F.)                                                                          Schedule                                                                             70 Bc 100 Bc                               ______________________________________                                        F      0.00          80     1g3    4:45  4:57                                 B      0.41          80     1g3    4:11  4:25                                 C      0.68          80     1g3    5:08  5:19                                 F      0.00         100     3g4    2:49  3:14                                 B      0.41         100     3g4    2:54  3:28                                 C      0.68         100     3g4    3:02  3:30                                 F      0.00         125     5g3    1:36  1:46                                 B      0.41         125     5g3    1:43  1:47                                 C      0.68         125     5g3    1:52  2:00                                 ______________________________________                                         .sup.1 Variations of 30 minutes or less in thickening time is considered      within normal experimental error.                                        

Cement F which does not contain the fluid loss additive of the presentinvention, thickened in 4 hours and 45 minutes when tested at 80° F.

Cements B and C which contained the additive of the present invention,thickened in 4 hours, 11 minutes; and 5 hours, 8 minutes; respectively.

Although at first glance it appears that the additive of the presentinvention retarded the rate at which Cement C solidified, this is notthe case.

Due to the large amount of experimental error inherent in the testingprocedures, cements which thicken within 30 minutes of each other areconsidered to have equivalent thickening rates. Therefore, the additiveof the present invention does not delay the rate at which cementslurries solidify.

EXAMPLE VII

This example presents data on fluid loss in cements as performedaccording to conventional API cement tests. The tests were performedaccording to appendix F with well-simulation as outlined in paragraph drelative to atmospheric pressure simulation. The results are recorded inTable VII.

                  TABLE VII                                                       ______________________________________                                        API Water Loss in Fresh Water, cc/30 minutes                                  polymer composition                                                           in weight %        125° F.                                             ID No.                                                                              AM/NAc/AMPS/NVP  cc/30 min.                                                                              conc. added                                  ______________________________________                                         1    3/15.5/61/20.5   275       0.24%                                         2    50/30/10/10      208       0.24%                                         3    37.1/18.2/33.1/11.1                                                                            413       0.24%                                         4    35/30/15/30      202       0.24%                                         5    15.6/9.4/25/50   738       0.24%                                         6    13.7/2.1/63.0/21.2                                                                             388       0.24%                                         7    5/55/30/10        77       0.24%                                         8    2/3/90/5         716       0.24%                                         9    5/20/15/60       376       0.24%                                        10    55/20/15/10      102       0.24%                                        11    60/10/10/20      148       0.24%                                        12    45/25/10/20      136       0.24%                                        13    45/20/15/20      108       0.24%                                        14    45/10/25/20      128       0.24%                                        15    35/10/35/20      135       0.24%                                        16    30/10/40/20      114       0.24%                                        17    30/15/35/20      110       0.24%                                        18    26.6/16.0/42.4/15                                                                              118       0.24%                                        19    25/15/40/20      114       0.24%                                        20    60/20/10/10       88       0.24%                                        21    35/15/30/20       88       0.24%                                        22    34/14/30/22       82       0.24%                                        23    33/14/28/25       91       0.24%                                        24    32/13/27/28       86       0.24%                                        25    23.5/14.0/37.5/25                                                                               90       0.24%                                        26    5/55/30/10        77       0.24%                                        ______________________________________                                         Note:-                                                                        Concentration of polymer added in % by weight of cement (BWOC).               AM = acrylamide                                                               NAc = sodium acrylate                                                         AMPS ™ = acrylamidomethylpropane sulfonate (trademark of Lubrizol)         NVP = nvinylpyrrolidone                                                  

This data indicates that these polymers are effective in reducing waterloss in drilling cements.

EXAMPLE VIII

This example presents data on fluid loss in cements as performedaccording to conventional API cement tests. The tests were performedaccording to appendix F with well-simulation as outlined in paragraph Drelative to atmospheric pressure simulation. The results are recorded inTable VIII.

                  TABLE VIII                                                      ______________________________________                                        API Water Loss in Fresh Water, cc/30 minutes                                  polymer composition                                                           in weight %        200° F.                                             ID No.                                                                              AM/NAc/AMPS/NVP  cc/30 min.                                                                              conc. added                                  ______________________________________                                         1    15.6/9.4/25/50   728       0.33%                                         2    13.7/2.1/63.1/21.1                                                                             814       0.33%                                         3    2/3/90/5         717       0.33%                                         4    55/20/15/10      115       0.33%                                         5    50/30/10/10      132       0.33%                                         6    37.1/18.2/33.1/11.1                                                                            100       0.33%                                         7    35/30/15/30      100       0.33%                                         8    18.8/11.2/30/40  260       0.33%                                         9    5/20/15/60       153       0.33%                                        10    5/55/30/10       103       0.33%                                        11    45/10/25/20      52        0.33%                                        12    60/20/10/10      56        0.33%                                        13    60/10/10/20      76        0.33%                                        14    50/20/10/20      77        0.33%                                        15    35/15/30/20      50        0.33%                                        16    32/13/27/28      55        0.33%                                        17    30/10/40/20      53        0.33%                                        18    26.6/16/42.4/15  52        0.33%                                        19    25/10/45/20      54        0.33%                                        20    25/15/40/20      50        0.33%                                        21    25/20/35/20      57        0.33%                                        22    20/15/45/20      56        0.33%                                        23    20/10/50/20      54        0.33%                                        24    15/10/55/20      58        0.33%                                        25    3/15.5/61/20.5   97        0.33%                                        26    34/14/30/22      46        0.33%                                        27    33/14/28/25      46        0.33%                                        28    30/15/35/20      47        0.33%                                        29    23.5/14/37.5/25  45        0.33%                                        30    35/10/35/20      54        0.33%                                        31    32/13/27/28      55        0.33%                                        32    45/25/10/20      56        0.33%                                        ______________________________________                                         Note:-                                                                        Cement slurries tested at 200° F. contain 35% silica sand BWOC (by     weight of cement) and concentration of polymer added is in % BWOC.            AM = acrylamide                                                               NAc = sodium acrylate                                                         AMPS ™ = acrylamidomethylpropane sulfonate (trademark of Lubrizol)         NVP = nvinyl pyrrolidone                                                 

This data indicates that these polymers are effective in reducing waterloss in drilling cements.

EXAMPLE IX

This example presents data on fluid loss in cements as performedaccording to conventional API cement tests. The tests were performedaccording to appendix F with well-simulation as outlined in paragraph drelative to atmospheric pressure simulation. The results are recorded inTable IX.

                  TABLE IX                                                        ______________________________________                                        API Water Loss in Fresh Water, cc/30 minutes                                  polymer composition                                                           in weight %        300° F.                                             ID No.                                                                              AM/NAc/AMPS/NVP  cc/30 min.                                                                              conc. added                                  ______________________________________                                         1    60/20/10/10      254       0.36%                                         2    55/20/15/10      259       0.36%                                         3    50/20/10/20      221       0.36%                                         4    45/25/10/20      227       0.36%                                         5    35/30/15/30      245       0.36%                                         6    15.6/9.4/25/50   1232      0.36%                                         7    13.6/2.1/63.1/21.2                                                                             1041      0.36%                                         8    5/20/15/60       1408      0.36%                                         9    2/3/90/5         1275      0.36%                                        10    60/10/10/20      138       0.36%                                        11    50/30/10/10      137       0.36%                                        12    45/20/15/20      172       0.36%                                        13    45/10/25/20      118       0.36%                                        14    37.1/18.7/33.1/11.1                                                                            154       0.36%                                        15    35/10/35/20      176       0.36%                                        16    30/10/40/20      124       0.36%                                        17    25/10/45/20      122       0.36%                                        18    20/10/50/20      106       0.36%                                        19    3/16/61/20       108       0.36%                                        20    35/15/30/20       86       0.36%                                        21    34/14/30/22       85       0.36%                                        22    33/14/28/25       84       0.36%                                        23    32/13/27/28       92       0.36%                                        24    30/15/35/20       91       0.36%                                        25    25/15/40/20       94       0.36%                                        26    25/20/35/20       78       0.36%                                        27    23.5/14.1/37.5/25                                                                               77       0.36%                                        28    20/15/45/20       90       0.36%                                        29    15/10/55/20       88       0.36%                                        30    5/55/30/10        44       0.36%                                        ______________________________________                                         Note:-                                                                        Cement slurries tested at 300° F. contain 35% silica sand BWOC (by     weight of cement) and concentration of polymer added is in % BWOC.            AM = acrylamide                                                               NAc = sodium acrylate                                                         AMPS ™ = acrylamidomethylpropane sulfonate (trademark of Lubrizol)         NVP = nvinyl pyrrolidone                                                 

This data indicates that these polymers are effective in reducing waterloss in drilling cements.

EXAMPLE X

This example presents data on fluid loss in cements as performedaccording to conventional API cement tests. The tests were performedaccording to appendix F with well-simulation as outlined in paragraph drelative to atmospheric pressure simulation. The results are recorded inTable X.

                  TABLE X                                                         ______________________________________                                        API Water Loss in 10% NaCl, cc/30 minutes                                     polymer composition                                                           in weight %        200° F.                                             ID No.                                                                              AM/NAc/AMPS/NVP  cc/30 min.                                                                              conc. added                                  ______________________________________                                         1    15.6/9.4/25/50   680       0.3%                                          2    13.6/2.1/63.1/21.2                                                                             1107      0.3%                                          3    5/55/30/10       1833      0.3%                                          4    2/3/90/5         1177      0.3%                                          5    60/10/10/20      238       0.3%                                          6    55/20/15/10      200       0.3%                                          7    50/30/10/10      212       0.3%                                          8    37/18/33/12      206       0.3%                                          9    3/15.5/61/20.5   272       0.3%                                         10    60/20/10/10      192       0.3%                                         11    50/20/10/20      150       0.3%                                         12    45/25/10/20      102       0.3%                                         13    35/10/35/20      115       0.3%                                         14    35/30/15/30      148       0.3%                                         15    30/10/40/20      109       0.3%                                         16    30/15/35/20      119       0.3%                                         17    27/16/43/15      120       0.3%                                         18    25/10/45/20      106       0.3%                                         19    20/10/50/20      118       0.3%                                         20    15/10/55/20      120       0.3%                                         21    45/20/15/20       98       0.3%                                         22    45/10/25/20       92       0.3%                                         23    35/15/30/20       96       0.3%                                         24    34/14/30/22       64       0.3%                                         25    33/14/28/25       72       0.3%                                         26    32/13/27/28       80       0.3%                                         27    25/15/40/20       80       0.3%                                         28    25/20/35/20       96       0.3%                                         29    23.5/14/37.5/25   84       0.3%                                         30    20/15/45/20       88       0.3%                                         ______________________________________                                         Note:-                                                                        Concentration of polymer added in % by weight of cement (BWOC).                AM = acrylamide                                                              NAc = sodium acrylate                                                         AMPS ™ = acrylamidomethylpropane sulfonate (trademark of Lubrizol)         NVP = nvinyl pyrrolidone                                                 

EXAMPLE XI

All polymers were prepared using a bulk solution polymerization with afree radical initiator in a stoichiometric excess (approximately 100%excess). The initator used was 2,2'-azobis(N,N'-dimethyleneisobutyramidine) dihydrochloride. The monomers wereadded in the desired weight percent ratio, with water being added toachieve the desired solids content. EDTA (ethylenediaminetetraaceticacid), a chelating agent, was also added in a stoichiomeric excess. Thesystem was throughly purged with an inert gas, and the monomers wereallowed to react at temperatures in the range of 20° to 60° C.

Reasonable variations can be made in view of the foregoing disclosurewithout departing from the spirit or scope of the present invention.

That which is claimed is:
 1. In a process of cementing a well with ahydraulic cement wherein said cement is pumped into the well bore andallowed to solidify wherein the improvement comprises admixing atetrapolymer, in amounts effective to control water loss wherein saidtetrapolymer is the polymerization product consisting essentially of:(a)about 30 weight percent of component A which is selected from the groupconsisting of 2-acrylamido-2-methylpropane sulfonic acid and salts of2-acrylamido-2-methylpropane sulfonic acid; (b) about 10 weight percentof component B which is N-vinyl-2-pyrrolidone; (c) about 5 weightpercent of component C which is acrylamide; and (d) about 55 weightpercent of component D which is selected from the group consisting ofacrylic acid and salts of acrylic acid.
 2. In a process of cementing awell with a hydraulic cement wherein said cement is pumped into the wellbore and allowed to solidify wherein the improvement comprises admixinga tetrapolymer, in amounts effective to control water loss wherein saidtetrapolymer is the polymerization product consisting essentially of:(a)about 20 weight percent to about 38 weight percent of component A whichis selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and salts of 2-acrylamido-2-methylpropane sulfonic acid;(b) about 20 weight percent to about 30 percent of component B which isN-vinyl-2-pyrrolidone; (c) about 23 weight percent to about 35 weightpercent of component C which is acrylamide; and (d) about 14 weightpercent to about 20 weight percent of component D which is selected fromthe group consisting of acrylic acid and salts of acrylic acid.
 3. In aprocess of cementing a well with a hydraulic cement wherein said cementis pumped into the well bore and allowed to solidify wherein theimprovement comprises admixing a tetrapolymer, in amounts effective tocontrol water loss wherein said tetrapolymer is the polymerizationproduct consisting essentially of:(a) about 28 weight percent to about38 weight percent of component A which is selected from the groupconsisting of 2-acrylamido-2-methylpropane sulfonic acid and salts of2-acrylamido-2-methylpropane sulfonic acid; (b) about 20 weight percentto about 25 percent of component B which is N-vinyl-2-pyrrolidone; (c)about 23 weight percent to about 34 weight percent of component C whichis acrylamide; and (d) about 14 weight percent to about 15 weightpercent of component D which is selected from the group consisting ofacrylic acid and salts of acrylic acid.
 4. In a process of cementing awell with a hydraulic cement wherein said cement is pumped into the wellbore and allowed to solidify wherein the improvement comprises admixinga tetrapolymer, in amounts effective to control water loss wherein saidtetrapolymer is the polymerization product consisting essentially of:(a)about 15 weight percent to about 45 weight percent of component A whichis selected from the group consisting of 2-acrylamido-2-methylpropanesulfonic acid and salts of 2-acrylamido-2-methylpropane sulfonic acid;(b) about 20 weight percent to about 30 percent of component B which isN-vinyl-2-pyrrolidone; (c) about 20 weight percent to about 45 weightpercent of component C which is acrylamide; and (d) about 10 weightpercent to about 20 weight percent of component D which is selected fromthe group consisting of acrylic acid and salts of acrylic acid.
 5. In aprocess of cementing a well with a hydraulic cement wherein said cementis pumped into the well bore and allowed to solidify wherein theimprovement comprises admixing a tetrapolymer, in amounts effective tocontrol water loss wherein said tetrapolymer is the polymerizationproduct consisting essentially of:(a) about 30 weight percent ofcomponent A which is selected from the group consisting of2-acrylamido-2-methylpropane sulfonic acid and salts of2-acrylamido-2-methylpropane sulfonic acid; (b) about 22 weight percentof component B which is N-vinyl-2-pyrrolidone; (c) about 34 weightpercent of component C which is acrylamide; and (d) about 14 weightpercent of component D which is selected from the group consisting ofacrylic acid and salts of acrylic acid.